Beau Trap (Grose 1811 Dictionary)

Beau Trap

A loose stone in a pavement, under which
water lodges, and on being trod upon, squirts it up, to the
great damage of white stockings; also a sharper neatly
dressed, lying in wait for raw country squires, or ignorant
fops.

Definition taken from
The 1811 Dictionary of the Vulgar Tongue,
originally by Francis Grose.